Researchers looked at 50+ years of studies to see if fermented foods like yogurt, kimchi, and miso can actually boost your vitamin levels. They found that certain bacteria in these foods can create extra vitamins, especially vitamin K2 and some B vitamins. Some fermented foods showed real promise—like natto (fermented soybeans) for vitamin K2 and certain cheeses for folate. However, scientists say we need more large-scale studies to prove these foods are a reliable way to fix vitamin deficiencies. The good news is that fermented foods appear safe and may help, but they shouldn’t replace other vitamin sources yet.

The Quick Take

  • What they studied: Whether eating fermented foods (foods made with helpful bacteria like yogurt, kimchi, and miso) can increase the vitamins in your body and improve your health.
  • Who participated: This review analyzed human studies from 1970 to 2024. The studies included healthy people and people with vitamin deficiencies, though specific numbers varied across different research projects.
  • Key finding: Certain bacteria in fermented foods can create extra vitamins, particularly vitamin K2 (found in natto) and folate/vitamin B9 (found in some cheeses). These vitamins actually entered people’s bodies and showed measurable effects in some studies.
  • What it means for you: Eating fermented foods may help boost certain vitamins, especially if you enjoy them anyway. However, don’t rely on them as your only source of vitamins yet—more research is needed. They’re a promising addition to a healthy diet, not a replacement for other vitamin sources.

The Research Details

Scientists reviewed all human studies published between 1970 and 2024 that tested whether fermented foods actually changed people’s vitamin levels. They looked for studies that measured vitamin amounts in blood or other body markers before and after people ate fermented foods. They followed strict rules from European food safety experts to make sure they only included high-quality research. This approach, called a ‘systematic narrative review,’ lets researchers summarize what we know across many different studies while being honest about what’s still unclear.

Instead of just looking at what happens in test tubes or with bacteria alone, this review focused only on studies with real people. This matters because your body doesn’t always absorb vitamins the same way in food as scientists might predict. By looking at human studies, researchers could see if fermented foods actually work in real life, not just in theory.

This review is thorough and careful—it searched decades of research and followed official guidelines. However, it found that many existing studies were small or didn’t compare fermented foods to other sources properly. The researchers were honest that we need bigger, better-designed studies to be really confident about recommendations. The fact that they found mixed results for some vitamins shows they weren’t cherry-picking only positive findings.

What the Results Show

The review found strong evidence for two specific fermented foods: natto (fermented soybeans) consistently improved vitamin K2 levels in people’s bodies, and certain cheeses naturally high in folate (vitamin B9) helped people absorb more of this vitamin. These weren’t tiny effects—they were measurable improvements in blood tests. The bacteria in these foods actually created extra vitamins during fermentation, and people’s bodies absorbed them.

For other B vitamins (like B1, B2, B3, B5, and B6), the evidence was weaker or mixed. Some studies showed improvements, but others didn’t, making it hard to draw firm conclusions. For vitamin B12, while some bacteria in fermented foods can make this vitamin, it’s unclear if people actually absorb enough from eating these foods to make a real difference.

The researchers discovered that several factors affect whether you actually get more vitamins from fermented foods: the specific type of bacteria used, how long the food ferments, what other ingredients are in the food, and even your own gut bacteria. This explains why one fermented food might work better than another.

An interesting finding was that your gut bacteria may play a role in how well fermented foods help your vitamin status. Some bacteria in your digestive system can also make vitamins, and fermented foods might help these bacteria do their job better. Additionally, the form the vitamin takes matters—some forms are easier for your body to use than others. The researchers also noted that the food itself (like whether it’s cheese, soy, or vegetables) changes how well your body absorbs the vitamins created during fermentation.

This review builds on decades of research showing that fermentation can increase vitamins in food. What’s new is the focus on whether these increases actually matter for human health. Previous research often stopped at showing bacteria could make vitamins; this review asks the harder question: do people actually get healthier? The findings suggest fermented foods are more promising than some skeptics thought, but less proven than enthusiasts claim.

The biggest limitation is that most existing studies are small and don’t follow the same methods, making it hard to compare results. Many studies didn’t have a control group (people eating regular, non-fermented versions of the same food) for comparison. Some studies only lasted a few weeks, which isn’t long enough to see if benefits stick around. The researchers found almost no studies on many fermented foods people actually eat regularly. Finally, most studies focused on vitamin amounts in blood rather than whether people actually felt healthier or had fewer symptoms of vitamin deficiency.

The Bottom Line

If you enjoy fermented foods like yogurt, kimchi, miso, or natto, eating them regularly appears safe and may help with certain vitamins—especially vitamin K2 if you eat natto. However, don’t count on fermented foods alone to fix a vitamin deficiency. If you’re concerned about vitamin levels, talk to a doctor and consider other reliable sources like supplements or a varied diet with plenty of vegetables, fruits, and proteins. For healthy people eating a decent diet, fermented foods are a nice addition but not essential.

People with known vitamin deficiencies should care about this research—it suggests fermented foods might help, but shouldn’t replace medical treatment. Vegetarians and vegans should pay attention, especially regarding vitamin B12 and K2. People who enjoy fermented foods can feel good about eating them. People with digestive issues might benefit since fermented foods contain helpful bacteria. However, people with certain food allergies or sensitivities should be cautious, and anyone with serious health conditions should check with their doctor.

If fermented foods do help, you’d likely see changes in blood vitamin levels within a few weeks to a few months of regular eating. However, feeling healthier or noticing symptoms improve might take longer—usually several months. Don’t expect overnight changes. The longer you eat fermented foods regularly, the more likely you’ll see sustained benefits.

Want to Apply This Research?

  • Track weekly servings of fermented foods (yogurt, kimchi, miso, natto, sauerkraut, tempeh) and note any changes in energy levels, mood, or how you feel. Aim for 2-3 servings per week and log which types you eat, since different fermented foods provide different vitamins.
  • Start adding one fermented food to your regular meals. If you don’t eat fermented foods now, try adding a small serving of plain yogurt to breakfast, a spoonful of miso to soups, or a side of kimchi to dinner. Make it a habit by pairing it with something you already do daily.
  • Over 3 months, track how consistently you eat fermented foods and note any changes in how you feel. If possible, get blood work done before and after to measure actual vitamin levels—this gives you real data. Keep notes on digestion, energy, and overall wellness to see if there are patterns.

This review summarizes research findings but is not medical advice. Fermented foods may support vitamin intake but should not replace prescribed vitamin supplements or medical treatment for vitamin deficiencies. If you have a diagnosed vitamin deficiency, are pregnant, nursing, have a compromised immune system, or take medications that interact with fermented foods, consult your healthcare provider before making dietary changes. This information is for educational purposes and should not be used to diagnose or treat any medical condition.